Breast cancer is the most common type of cancer in women and accounts for approximately 15% of the cancer-related deaths in the U.S. HER-2, also described as c-erbB-2 or neu, is a cell surface receptor that belongs to a family of receptors that have been shown to promote cell growth, differentiation, and survival. HER-2 expression on breast cancer cells is associated with particularly aggressive breast cancer cancers and is detected in about 25 to 30% of the diagnosed breast cancer cases. HER-2 expression is associated with poor outcome, aggressive tumor behaviors, and resistance to some therapeutic agents, including the taxanes, paclitaxel and docetaxol. However, the molecule is also a target for the monoclonal antibody therapy, herceptin (also known as trustazumab). The use of herceptin, in HER-2 expressing ductal carcinoma of the breast, in combination with chemotherapy, results in an increase in disease free survival and in disease free recurrence. HER-2 degradation, resulting from its engagement with either egf or herceptin, appears to increase sensitivity to docetaxol and herceptin-induced down regulation and has been linked to improved clinical responses. Recent studies by Slamon, et al, have shown that HER-2 overexpression promotes the growth and malignancy of mammary epithelial cells, in part, by conferring resistance to the growth inhibitory effects of TGF-beta. Interestingly, however, their work also shows that HER-2 and TGF-beta signaling pathways can cooperate to promote especially aggressive disease behavior in the context of a highly invasive breast tumor model (Wilson C A et al. 2005. HER-2 overexpression differentially alters transforming growth factor-beta responses in luminal versus mesenchymal human breast cancer cells. Breast Cancer Res. 2005;7(6):R1058-79).